The Medicare Part D coverage gap affects approximately 3 million beneficiaries per year, including many older adults with diabetes. Beneficiaries who enter the gap are at risk of cost-related non-adherence, but there are no published studies examining the consequences of gap entry on adherence and clinical outcomes among older adults with diabetes. The proposed award has 3 specific aims: to examine whether entering the coverage gap affects 1) medication adherence and rates of switching to generic medications, 2) hemoglobin A1c and low-density cholesterol (LDL) lipoprotein levels, and 3) the likelihood of an emergency department visit as well as the likelihood of a preventable hospitalization. This work will use 2006 and 2007 50-state data from UnitedHealth, the largest for-profit Part D provider in the United States. We already have prescription claims as well as inpatient, outpatient, and emergency department utilization claims for UnitedHealth enrollees, and are finalizing an existing agreement to obtain data on intermediate outcomes. The analytic sample will include Medicare Advantage Part D (MAPD) plan enrollees with diabetes who are =65 years of age. We will use existing algorithms to identify patients with diabetes based on prescription fills for an anti- glycemic medication, and use prescription claims to track drug costs and determine dates of gap entry and gap exit. We will calculate medication adherence using the proportion of days' covered (PDC), and use ICD-9 codes to identify hospitalizations related to diabetes-related complications. We will conduct multivariate analyses (as well as propensity score analyses) to address each of the specific aims and compare each study outcome between beneficiaries who entered the gap by August 1 with beneficiaries who did not enter the gap during that year. All analyses will be stratified by benefit generosity (no coverage during the gap versus generic-only coverage during the gap). The proposed analyses will provide needed policy relevant data with direct implications for older adults with diabetes in the US, and also inform the development of an intervention to reduce adverse clinical events by delaying or preventing patients from entering the coverage gap. PUBLIC HEALTH RELEVANCE: This study will examine the impact of the Medicare Part D coverage gap on medication use and clinical outcomes, including metabolic control, emergency department use, and hospitalizations, among older adults with diabetes in managed care. The analyses will include patients with no drug coverage during the gap as well as generic-only drug coverage during the gap, and will provide important information about the effect of this policy on this vulnerable population.